A fuel tank opening-closing device, as shown in JP-A 2008-49952, includes a shutter mechanism that opens and closes the inlet of a tank opening forming member (flap valve mechanism), and a locking mechanism that allows the opening operation of the shutter mechanism. The locking mechanism includes a nozzle guide part inner diameter positioning part (nozzle detection mechanism) and a lock member, and by moving the lock member from the locked position to the unlocked position by being pushed by the tip of inner diameter side of the fueling nozzle, the opening operation of the shutter mechanism is allowed, the shutter opens by pushing using the tip of the fueling nozzle, and this is how fueling is performed.
However, with related fuel tank opening-closing devices, because a lock member and inner diameter positioning part are incorporated in the shutter mechanism, the constitution and arrangement are complex, and there was the problem of requiring a strict dimensional tolerance to guide the fueling nozzle to the inner diameter positioning part which is determined by the fueling nozzle inner diameter.